Field of the Invention
The present invention relates to a filtering processing technique.
Description of the Related Art
Conventionally, when outputting after performing image forming, local (vicinity) image processing such as spatial filtering is performed. Local image processing is image processing that uses a plurality of reference pixels (pixels that are a processing target and pixels in a vicinity thereof) included in a reference area of an input image. For example, in spatial filtering such as edge enhancement processing or blurring processing, a value of a pixel that is to be a processing target is obtained by a product-sum operation between values of reference pixels and filter coefficients. Because a number of product-sum operations (hereinafter, a calculation amount is used as an abbreviated name) is equal to a number of reference pixels, an increase in the calculation amount frequently becomes a problem if a size of a reference area (the size of a filter) is set to be large when trying to implement desired characteristics.
Accordingly, as a conventional technique for solving this problem, there is the technique disclosed in Japanese Patent Laid-Open No. 2005-167831. That is, by using an interlaced image (an image where lines are thinned) for an input image and setting a filter coefficient for lines not input to 0, the number of reference pixels used in product-sum operations (hereinafter, an abbreviated name of tap number is used) is reduced while maintaining the size of the reference area for the filter.
However, because an upper limit for a frequency band in which it is possible to perform control by spatial filtering well decreases as the spacing of reference pixels spreads, if the spacing of reference pixels spreads due to reducing the tap number without changing the size of the reference area, high frequency controllability decreases.